With the size of a MOSFET shrinks, the device is subjected to even more severe negative effects such as a short channel effect of the device and etc. after entering a nanometer scale, which causes an off-state leakage current of device increase. Meanwhile, since a subthreshold slope of a conventional MOSFET is limited by the thermoelectric potential and thus cannot be reduced synchronously as the size of device decreases, there is a theoretical limit at 60 mV/dec, causing that the leakage current further increases as the reduction of the supply voltage, and thereby increasing the power consumption of the device. The power consumption issue has now become one of the most serious problems in limiting the scaling down of the device.
In the field of ultra-low voltage and power consumption, a device using a new switching mechanism to obtain ultra-steep subthreshold slope and a process method for fabricating the same has become a focus of attention in recent years. Since such device is not restricted by the thermoelectric potential and thus can break the subthreshold slope limit of the conventional MOSFET, and thus has great advantages when applied into in the low power device. Among them, a tunneling field effect transistor (TFET) has attracted widespread attentions due to a very low leakage current and an ultra steep subthreshold slope. Unlike the conventional MOSFET, doping types of a source and a drain of the TFET are opposite to each other, the TFET can be turned on by a band-to-band tunneling of a reverse-biased P-I-N junction under control of a gate, and thus it can operate at a lower voltage, thus is suitable for being applied into the field of low voltage and low power consumption. However, the TFET faces a problem of a small on-state current due to constraints in the tunneling probability and tunneling area of a source junction, which is far less desirable than that of traditional MOSFET. Moreover, the TFET has an ambipolar effect, greatly limiting the application of the TFET.